Electric arc furnaces (EAFs) make steel by using an electric arc to melt charges of scrap metal, hot metal, iron based material, or other metal materials placed within the furnace. Modern EAFs may also make steel by melting direct reduced iron (“DRI”) combined with the hot metal from a blast furnace. In addition to the electrical energy of the arc, chemical energy can be provided by auxiliary burners using fuel and an oxidizing gas to produce combustion products with a high heat content to assist the arc.
If the EAF is used for melting scrap, the scrap burden is charged by dumping it into the furnace through the roof opening from buckets, which also may include charged carbon and slag forming materials. A similar charging method using a ladle for the hot metal from a blast furnace may be used along with injection of the DRI by a lance to produce the burden. Additionally, these materials can be added through other openings in the furnace.
In the melting phase, the electric arc and burners melt the burden into a molten pool of metal, termed an iron carbon melt, which accumulates at the bottom or hearth of the furnace. Typically, after a flat bath has been formed by melting of all introduced burden, the electric arc furnace enters a refining and/or decarburization phase. In this phase, the metal continues to be heated by the arc until the slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag.
Before the melt is poured out of the furnace, therefore, it is necessary to remove the slag and impurities from the surface of the melt. It can also be desirable to take samples of the melt to check, among other things, the chemistry of the melt, carbon and oxygen levels, and temperature. Conventionally, this is done by opening a slag door located in the furnace sidewall. Due to their design, however, opening a conventional slag door enables large amounts of heat to radiate from the furnace and significant amounts of cold outside air to infiltrate the furnace shell, resulting in longer melt cycles and higher production costs.
In addition, conventional slag doors are generally mounted some distance away from the sidewall of the furnace and connected thereto with a corridor or tunnel. During the charging and melting cycle, scrap, slag, and other debris can accumulate in the slag door tunnel. To gain access to the melt to deslag or test the melt, therefore, the debris is cleared from the tunnel. This is done by opening the door and using a large ram installed on a truck to push the debris into the melt. The door is then closed and additional time is given for the debris to become molten and incorporated into the melt. The additional time required to melt the debris increases melt cycle times and reduces efficiency.
In addition to the obvious dangers of opening the slag door while the furnace is in operation, pushing debris into the hot melt can present additional dangers. The first, most obvious, danger is the possibility that pushing debris into melt will splash molten metal onto workers and/or equipment causing damage and/or injury. In addition, during operation, the melt pool in the furnace can become stratified. In other words, when fully liquefied, the melt can contain layers of steel with higher concentrations of entrained carbon near the bottom of the melt and layers with higher concentrations of entrained oxygen near the top of the melt. Pushing the debris from the breast of the furnace into the melt can cause these stratified layers to mix quickly causing a violent reaction as the carbon and oxygen combine and release carbon dioxide. This can create a roiling “boil-over” type effect that presents significant danger to workers and equipment.
In addition, some past designs for slag doors have comprised doors hung on side-mounted hinges. After deslagging, a significant portion of the slag can solidify in and around the doorway and tunnel. This slag build-up can make it difficult or impossible to close a side-mounted door completely because the bottom of the slag door drags on the remaining slag. Leaving the slag door open can result in significant heat losses as the EAF's exhaust system draws cool outside air through the slag door and into the furnace.
What is needed, therefore, is a slag door configured to be mounted as close as possible to the sidewall of the EAF. This can reduce or eliminate the tunnel between the slag door and the furnace threshold. This, in turn, eliminates the build-up of slag and debris in the tunnel, which must be cleared prior to deslagging or testing. What is also needed is a door that can be closed and substantially sealed despite the presence of slag and/or other debris on the threshold of the door. It is to such a slag door that embodiments of the present invention are primarily directed.